1. Field of the Invention
This invention relates to a stencil printing ink container, which is capable of being releasably fitted to a stencil printing apparatus in order to furnish ink to the stencil printing apparatus.
2. Description of the Related Art
Stencil printing apparatuses for performing printing operations by use of thermosensible stencil paper have heretofore been known. With the stencil printing apparatuses, a thermal head comprising fine heating elements arrayed in a line is brought into contact with stencil paper, and the stencil paper is conveyed by a platen roller, or the like, while the heating elements are being energized. In this manner, a perforation image in accordance with image information is formed on the stencil paper. Thereafter, the stencil paper, on which the perforation image has been formed, is wound around a printing drum. Also, printing paper is pushed by a pushing member, such as a press roller, against an outer circumferential surface of the drum and moved. In this manner, ink is oozed out through an opening area of the drum and perforations of the stencil paper and transferred onto the printing paper. A printed image is thus formed on the printing paper.
In order to cope with reduction in diameter of plate making perforations of the stencil paper for obtaining a precise printed image, or in order to enhance the printing speed by enhancing infiltrating characteristics of the ink into the printing paper, it is often desired that a viscosity of the ink used be set at a low viscosity. In particular, in cases where the ink viscosity with respect to a region of a shear rate of at most 100 secxe2x88x921 is set at a low viscosity, the ink having been transferred onto the printing paper is capable of quickly infiltrating into the printing paper, and printed paper free from an ink offset to the back of the paper is capable of being obtained.
Conventional ink furnishing means of the stencil printing apparatuses comprises an ink furnishing roller, a distributor, and a doctor roller. The ink furnishing roller is located within the printing drum and is supported between side plates which stand facing each other. The ink furnishing roller is capable of rotating around its center axis. The distributor is located on the ink furnishing roller and supplies the ink onto the ink furnishing roller. The doctor roller is located at a predetermined spacing from the ink furnishing roller and controls the thickness of an ink film, which is formed around the outer circumferential surface of the ink furnishing roller. An example of the distributor comprises parallel tubular members having a plurality of holes having a small diameter. A different example of the distributor comprises a plurality of nozzles. The ink is sucked by an ink pump from an ink container and supplied dropwise through the distributor onto the ink furnishing roller. An ink accumulating area is formed at a wedge-shaped region between the ink furnishing roller and the doctor roller. The ink is furnished through a space between the ink furnishing roller and the doctor roller into the printing drum. Such that the ink may be furnished uniformly, a predetermined amount of the ink is always held at the ink accumulating area.
Ordinarily, a W/O type of emulsion ink comprising 10 wt % to 50 wt % of an oil phase and 90 wt % to 50 wt % of an aqueous phase is utilized for the stencil printing apparatuses. In cases where the stencil printing apparatuses are left to stand for a long period of time instead of being used for the printing, since the ink accumulated at the ink accumulating area is exposed to air, water contained in the ink is vaporized, and a pigment concentration in the ink becomes high. Therefore, the ink having a low viscosity remains at the ink accumulating area. In cases where fresh ink is furnished to the ink accumulating area, the remaining ink and the fresh ink cannot easily mix with each other, and therefore it often occurs that nonuniformity in image density occurs on the printed paper. Nonuniformity in image density occurs markedly in the cases of ink, which has a comparatively high viscosity with respect to the region of the shear rate of at most 100 secxe2x88x921.
As an example of an ink container utilized for the stencil printing apparatuses, there has heretofore been known an ink container (a BIC type of an ink container) comprising an outside casing formed from a corrugated board, or the like, and a flexible inside bag accommodated within the outside casing. An ink injecting tube, which is formed at an end of the inside bag, is projected from the region within the outside casing to the exterior of the outside casing, and the projected end of the ink injecting tube is closed with a cap. Also, as a different example of an ink container utilized for the stencil printing apparatuses, there has heretofore been known an ink container (a piston type of an ink container) comprising a cylinder, which has a circular cylinder-like shape and is provided with an ink discharge opening section at an end, and a piston, which is located within the cylinder. In particular, the piston type of the ink container has the advantages in that the amount of the ink, which remains within the ink container after the ink suction has been performed until ink suction and furnishing cannot be conducted any more, is smaller than 8 the amount of the remaining ink in the cases of the BIC type of the ink container, and therefore the ink is capable of being used efficiently. The ink discharge opening section of the piston type of the ink container is sealed by a thread type of cap. When the piston type of the ink container is to be used, the user removes the cap from the ink discharge opening section, inserts the ink container through a container holder on the side of the main body of the stencil printing apparatus, and fits the ink discharge opening section of the ink container to an ink suction opening section on the side of the main body of the stencil printing apparatus. In this manner, the piston type of the ink container is used.
However, with the conventional piston type of the ink container, it is considered that the problems described below occurs in cases where the ink container is filled with ink having a comparatively low viscosity with respect to the region of the low shear rate described above and used. Specifically, in cases where the user removes the cap from the ink discharge opening section of the ink container and holds the ink container with the ink discharge opening section facing down, the ink drips down from the ink discharge opening section of the ink container and soils the hands or clothes of the user, the region within the stencil printing apparatus, a floor surface within a room in which the stencil printing apparatus is located, or the like.
In order for the problems described above to be solved, a structure, in which a valve opened through engagement with a main body of a printing machine is located within an ink discharge opening section of an ink container, has been proposed in, for example, Japanese Unexamined Patent Publication No. 2000-318288. However, the proposed ink container has the problems in that the valve located within the ink discharge opening section of the ink container is constituted of a fine member and therefore has a strong probability of being broken, and in that the cost cannot be kept low due to the increased number of parts.
Also, a method of setting an ink container, wherein an ink container is set in a main body of a printing machine with an ink discharge opening section of the ink container facing up, such that a user may not locate the ink container with the ink discharge opening section facing down in a state in which the ink discharge opening section is released, has been proposed in, for example, Japanese Unexamined Patent Publication No. 2000-272097. However, with the proposed method of setting an ink container, limitation is imposed upon the size of the ink container which is capable of being utilized. However, stencil printing apparatuses are used primarily in applications in which a large number of prints are formed from a single stencil paper. Therefore, the ink containers for use in the stencil printing apparatuses are designed with the intention of quickly furnishing a larger amount of ink than in the cases of ordinary business equipment, and the sizes of the ink containers are set to be comparatively large such that the amount of the ink loaded into a single ink container may fall within the range of 500 ml to 1,500 ml. Accordingly, with the proposed method of setting an ink container, the setting of the ink containers in the stencil printing apparatuses cannot be performed satisfactorily unless the diameter and the length of the drum are set at markedly large values.
The primary object of the present invention is to provide a stencil printing ink container, which is free from problems in that, in cases where ink having a low viscosity is accommodated within the ink container, the ink drips down from an ink discharge opening section of the ink container at the time of setting of the ink container into a stencil printing apparatus and at the time of removal of the ink container from the stencil printing apparatus.
The present invention provides a stencil printing ink container, comprising:
i) a cylinder having an approximately circular cylinder-like shape, an area of one end of the cylinder, which area is other than an ink discharge opening section, being closed with an end wall, the other end of the cylinder being open, and
ii) a piston, which is capable of undergoing a sliding movement in an axial direction of the cylinder and along an inner circumferential surface of the cylinder,
the stencil printing ink container being filled with ink, which has a viscosity of at most 7.5Paxc2x7s with respect to a shear rate of 100 secxe2x88x921 and at a temperature of 23xc2x0 C., and satisfying relationship represented by the formula:   r  ≦                    (                              3.0            xc3x97                                          10                                  -                  6                                            ·              8                        ⁢                          xe2x80x83                        ⁢                          η              ·              L              ·                              R                2                                                          9.8            ⁢                          (                                                                                          1                      /                      η                                                        ·                  W                                -                N                            )                                      )                    1        /        4              ⁢          xe2x80x83        ⁢    or    ⁢                  xe2x80x83            ⁢              xe2x80x83              ⁢    0    ≧                              1          /          η                    ·      W        -    N  
wherein R represents the inside radius, in units of m, of the cylinder, r represents the inside radius, in units of m, of the ink discharge opening section, L represents the length, in units of m, of the ink discharge opening section, W represents the weight, in units of kg, of the ink filled in the stencil printing ink container, N represents the sliding movement starting load, in units of kgf, of the piston, and xcex7 represents the viscosity, in units of Paxc2x7s, of the ink, which is filled in the stencil printing ink container, with respect to a shear rate of 100 secxe2x88x921 and at a temperature of 23xc2x0 C.
In the stencil printing ink container in accordance with the present invention, the viscosity of the ink is the viscosity with respect to a shear rate of 100 secxe2x88x921 and at a temperature of 23xc2x0 C. Unless otherwise specified, the term xe2x80x9cviscosity of inkxe2x80x9d as used herein means the viscosity with respect to a shear rate of 100 secxe2x88x921 and at a temperature of 23xc2x0 C.
The stencil printing ink container in accordance with the present invention should preferably be modified such that the ink discharge opening section is provided with a conical tapered area.
Also, the stencil printing ink container in accordance with the present invention should preferably be modified such that a position of the ink discharge opening section is shifted outwardly from a center point of the one end of the cylinder. Further, in such cases, the stencil printing ink container in accordance with the present invention should more preferably be modified such that the stencil printing ink container is used in a stencil printing apparatus, in which the stencil printing ink container is set horizontally to an ink suction opening section of the stencil printing apparatus with the ink discharge opening section being positioned more upward than the center point of the one end of the cylinder.
Furthermore, the stencil printing ink container in accordance with the present invention should preferably be modified such that the ink discharge opening section is cut obliquely. Also, in such cases, the stencil printing ink container in accordance with the present invention should more preferably be modified such that the stencil printing ink container is used in a stencil printing apparatus, in which the stencil printing ink container is set horizontally to an ink suction opening section of the stencil printing apparatus with the end of the ink discharge opening section facing upward. The expression of xe2x80x9can end of an ink discharge opening section facing upwardxe2x80x9d as used herein means that the stencil printing ink container is positioned such that the obliquely cut area of the ink discharge opening section stands facing upward.
The stencil printing ink container in accordance with the present invention comprises the cylinder having the approximately circular cylinder-like shape, the area of one end of the cylinder, which area is other than the ink discharge opening section, being closed with the end wall, the other end of the cylinder being open. The stencil printing ink container in accordance with the present invention also comprises the piston, which is capable of undergoing the sliding movement in the axial direction of the cylinder and along the inner circumferential surface of the cylinder. Further, the stencil printing ink container is filled with ink, which has a viscosity of at most 7.5 Paxc2x7s with respect to a shear rate of 100 secxe2x88x921 and at a temperature of 23xc2x0 C. Furthermore, the stencil printing ink container satisfies the relationship represented by the formula:   r  ≦                    (                              3.0            xc3x97                                          10                                  -                  6                                            ·              8                        ⁢                          xe2x80x83                        ⁢                          η              ·              L              ·                              R                2                                                          9.8            ⁢                          (                                                                                          1                      /                      η                                                        ·                  W                                -                N                            )                                      )                    1        /        4              ⁢          xe2x80x83        ⁢    or    ⁢                  xe2x80x83            ⁢              xe2x80x83              ⁢    0    ≧                              1          /          η                    ·      W        -    N  
wherein R represents the inside radius, in units of m, of the cylinder, r represents the inside radius, in units of m, of the ink discharge opening section, L represents the length, in units of m, of the ink discharge opening section, W represents the weight, in units of kg, of the ink filled in the stencil printing ink container, N represents the sliding movement starting load, in units of kgf, of the piston, and xcex7 represents the viscosity, in units of Paxc2x7s, of the ink, which is filled in the stencil printing ink container, with respect to a shear rate of 100 secxe2x88x921 and at a temperature of 23xc2x0 C.
Therefore, with the stencil printing ink container in accordance with the present invention, the problems are capable of being prevented from occurring in that, in cases where ink having a low viscosity with respect to a region of a low shear rate is accommodated within the ink container, the ink drips down from the ink discharge opening section of the ink container when the ink discharge opening section of the ink container is positioned so as to stand facing down at the time of the setting of the ink container into the stencil printing apparatus.
With the stencil printing ink container in accordance with the present invention, wherein the ink discharge opening section of the ink container is provided with the conical tapered area, the ink flowing out from the ink container is capable of being temporarily retained at the conical tapered area. Therefore, the dripping of the ink from the ink discharge opening section is capable of being restricted for a long time.
The stencil printing ink container in accordance with the present invention may be modified such that the position of the ink discharge opening section is shifted outwardly from the center point of the one end of the cylinder, and the stencil printing ink container is used in the stencil printing apparatus, in which the stencil printing ink container is set horizontally to the ink suction opening section of the stencil printing apparatus with the ink discharge opening section being positioned more upward than the center point of the one end of the cylinder. In such cases, the pressure of the ink exerted upon the ink discharge opening section of the ink container is capable of being kept low. Therefore, the dripping of the ink from the ink discharge opening section is capable of being restricted more efficiently.
Also, the stencil printing ink container in accordance with the present invention may be modified such that the ink discharge opening section is cut obliquely, and the stencil printing ink container is used in the stencil printing apparatus, in which the stencil printing ink container is set horizontally to the ink suction opening section of the stencil printing apparatus with the end of the ink discharge opening section facing upward. In such cases, since the oblique cut area of the ink discharge opening section is positioned so as to stand facing upward, the dripping of the ink from the ink discharge opening section is capable of being restricted more efficiently.